| Microstrip antennas are widely used in various wireless communication systems due to its small size and easy integration.However,with the improvement of integrated circuit technology,the microstrip antenna is gradually miniaturized and integrated,thus the electromagnetic thermal effect caused by the dielectric loss in the material can no longer be ignored.On the other hand,there is very little research on this topic internationally.Therefore,it is necessary to analyze the electromagnetic thermal effect of microstrip antennas.In order to analyze the electromagnetic thermal effect of microstrip antennas,this thesis firstly studies and establishes the generalized function analysis model of finite element method(FEM),and then studies the introduction of domain decomposition method(DDM)to transform the complex large unknown problem into small unknown problem with multiple sub-domains to solve,so as to improve the analysis efficiency of electromagnetic thermal effect of complex electric large size structure such as large microstrip antenna arrays and solve the problem of difficult solution by FEM.This thesis will introduce the following aspects:Firstly,this thesis introduces the basic theory of FEM and the general flow of FEM,describes the selection of electromagnetic and thermal control equationst,the choices of different basis function discretizations for the vector electric field and the scalar temperature field,as well as the transformation of the control equations into the finite element linear system of equations in frequency and time domains by means of variational principle,electromagnetic absorption boundary condition and thermal convection boundary condition.Then the basic principles of electromagnetic thermal effects are discussed briefly.Secondly,based on the steady-state conduction equation,appropriate thermal boundary conditions are brought in to construct a finite element linear system for the steady-state thermal effect of the microstrip antenna.For the transient electromagnetic thermal effect,the differential approximation is carried out before the finite element matrix construction for the transient heat transfer equation to realise the numerical model for the analysis of the electromagnetic thermal effects of microstrip antennas.Then the electromagnetic thermal effect of three typical microstrip antennas are modelled and characterised.The factors affecting the electromagnetic thermal effect of microstrip antennas are analysed,including the operating frequency,the material of the substrate,and the plate thickness.Finally,in order to improve the efficiency in solving the electromagnetic thermal effects analysis of large microstrip antenna arrays,DDM is incorporated.The algorithm first divides the solution domain into several non-overlapping sub-domains.Then continuous boundary conditions and Lagrange multiplier at the boundary surfaces of adjacent sub-domains are described to ensure the continuity of the field.Afterwards,the field distribution of each sub-domain can be obtained by back-substituting the Lagrange multiplier into each sub-domain.This thesis provides a reference and insight into the design of microstrip antennas from the perspective of electromagnetic thermal effects. |
